Segmented casing for kaolin melting furnace



' Feb. 17, 1959 J -rw e 2,874,201

SEGMENTED CASING FOR KAOLIN MELTING FURNACE Filed Nov. 8, 1955 FIG.2

United States Patent SE GMENTED CASING FOR KAOLIN MELTING FURNACEFrederick J. Hartwig, Alliance, Ohio, assignor to The Babcock & WilcoxCompany, New York, N. Y., a corporation of-New Jersey ApplicationNovember 8, 1955, Serial No. 545,590

3 Claims. (Cl. 13--23) This invention relates to electric resistancefurnaces for melting refractory mineral materials and, moreparticularly, to an improved construction of such furnaces providing foreasy disassembly of the furnace for'inaintenance, inspection and repairof replacement of parts.

The melting of such refractory mineral materials is a prerequisite forforming mineral wool. The minerals commonly employed for the manufactureof mineral wool are natural wool rock (calcareous shale or argilaceouslimestone), common shale, and combinations of calcareous and siliceousmaterials, such as metallurgical furnace slag. All such materials have afusion point in the range of l500-2500 F.

One of the principal uses of mineral wool of the character described isfor heat insulation. The upper use temperature limit for such materialis determined by the temperature'at which recrystallization occurstherein to an extent that embrittlement and loss of strength in thefibers result. At this temperature, known as the devitrificationtemperature, the material changes from a'glassy to a crystallinestructure. Tests of the best known commercial brands of mineral woolhave shown none in satisfactory condition after a twenty-four hourexposure at 1350 P. due to excessive recrystallization at thattemperature. The manufacturers recommended upper use temperature limitsfor these mineral wools are therefore in the range of 900-l200 F.

As disclosed in Patent No. 2,467,889, a mineral wool having an upper usetemperature limit in the range of l50(l2300 F. can be formed by usingkaolin as a starting material. Kaolins have a fusion point of about 3245F. The mineral wool is formed by melting the kaolin, which may beinitially in the form of pieces of grog or clinker made from calciningthe raw material to eliminate the water of combustion. The moltenmaterial is withdrawn from the furnace as a stream or a series ofdroplets and subjected to a high velocity jet of air or steam whichblows the droplets into long fibers.

In the production of mineral wool from molten refractory materials, itis desirable to tap the furnace continuously, rather than to tapintermittently, as in batch melting. This is particularly true in thecase of high melting point refractory materials, such as kaolin, as theperiodic shutting down of the furnace heating in order to pour batchesof the molten material results in solidification of the charge in whichthe electrodes or other heating elements may be imbedded. In turn, thisintroduces operating difficulties in re-starting the furnace.

In addition, it is difficult, if not impossible, to pour the moltenmaterial at a precise location when pouring by tilting the furnace, aswell as being very difficult to precisely control the pour rate. Allthese criteria dictate the need for a type of furnace construction inwhich the refractory material, such as kaolin, can be continuously andprogressively melted and tapped at a uniform rate over as long a periodof time as possible.

In accordance with the present invention, the kaolin,

or other refractory material to be used to form a mineral wool, ismelted in an electric resistance melting furnace. This furnace comprisesa generally cylindrical metal shell having a metal bottom and an opentop, the interior of the shell being lined with refractory brick, for atleast part of the distance from its bottom plate toward its open top.Three main electrodes are mounted through the walls of the furnace, andare connected to a threephase supply of alternating current of therequired capacity. The bottom plate has a central opening through whichthe molten kaolin may be tapped.

After a production run of a given duration, the time length of which isvariable from several hours to several days or weeks, it is generallynecessary to shut down the furnace for inspection, maintenance orrepair. When the furnace is thus shut down, themolten kaolin solidifies,generally making a solid mass of refractory including the solidifiedkaolin and the lining of the furnace. It is necessary to disassemble thefurnace in order to recover usable portions of the electrodes andtapping assembly.

The furnace construction of the present invention is particularlydesigned to facilitate such disassembly and subsequent re-assembly ofthe furnace. To this end, the metal shell or casing is formed of aplurality-preferably three-of upright segmental cylindrical sectionsjoined, with their adjacent edges in circumferentially spaced relation,by bolted connectors. This provides upright slots through which the mainelectrode assemblies may be mounted radially of the furnace. Eachsegment has a horizontal flange adjacent its lower edge, these flangesforming a shelf supporting an annular metal bottom plate.

The tapping assembly is-supported through the bottom plate-by mountingit detachably to the undersurface of the bottom plate. The interior ofthe furnace is partly or completely lined with built up refractoryshapes supported on the bottom plate.

For an understanding of the invention principle, reference is made tothe following description to a typical embodiment thereof as illustratedin the accompanying drawing. In the drawing:

Fig. 1 is a diametric sectional view of the furnace;

Fig. 2 is an elevation view of the furnace casing;

Fig. 3 is a diametric sectional view of the furnace casing; and

Fig. 4 is a partial axial sectional view of the furnace illustrating thesupport for the bottom plate.

Referring to the drawings, the electric resistance melting furnacecomprises a generally cylindrical and upright metal casing 15 comprisingthree cylindrical segments 15A, 15B and 15C detachably interconnected attheir adjacent upright edges to leave longitudinal slots therebetween toreceive the main electrodes 30. Casing 15 has an angle 16 welded to itsinner surface adjacent its bottom edge, this angle comprising separatearcuate angles on each of the three cylindrical segments. Angle 16serves as a shelf to support a flat annular metal bottom plate 17 of thefurnace, plate 17 having a central circular opening 18 therein. It willbe noted that the furnace casing is thus an easily assembled anddisassembled composite structure of the casing segments and the bottomplate.

The interior of the metal casing is lined by built-up refractory shapesproviding a relatively thick refractory lining 21 on bottom plate 17 anda relatively thick wall lining 22. The wall lining may be carried to theupper end of furnace 10, but it is usually terminated just above themain electrodes with the slots between the casing segments, above theWall lining, being suitably closed, as by removable metal strips.

The main electrods 30 may be mounted through special shape refractorybrick guides 25 aligned through each of the three slots in casing 15.The tapping assembly is mounted coaxially with the bottom furnaceopening 18.

The construction of electrodes 30 and of the tapping assembly forms thesubject matter of my co-pending application Serial No. 547,917, filedIJovernberfZl, 1955, now'Patent N0. 2,817,695,.issued December 24, 1957.

Referring more particularly to Figs. 2 and 3 each casing section 15A,158 or 15C is in the form of an are or segment of a cylinder, and has anarcuate length of substantially 120. The casing sections are bent fromrelatively thin steel plate, and each section has a relatively thickersteel flange 26 welded to its upper end and angles 27 welded along eachedge and braced by vertically spaced stiifeners or supports 28 extendingbetween the outer surface of the section and the inner surfaces of theangle and welded thereto. At'its lower inner edge, each section has anangle 16 welded thereto to removably support bottom plate 17.

Adjacent the top and bottom ends of the casing section vertically spacedstops 31 are welded to the outer leg of angles 27 to act as locators-forstraps 32 secured by bolts 33 to flanges 27. These straps detachablysecure the casing sections together in circumferentially spaced relationwith slots 34 between adjacent sections to receive electrodes 30 mountedin guides 25. After the sections are thus interconnected, plate 17 ispositioned on flanges 16 and refractory lining 21, 22 put in place.

After completion of a run, the power is turned off, and after thefurnace has completely cooled, any water and electrical connections aredisconnected from electrodes 30 and the tap assembly. Casing 15 is thendisassembled from the refractory mass and the solidified melt is splitwith a sledge hammer or the like. Usable portions of the electrodes andtapping assembly may then be recovered.

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the inventionprinciple, it will be understood that the invention may be embodiedotherwise without departing from such principle.

What is claimed is: v p

1. In a furnace for melting refractory material, an outer casingcomprising a plurality of separate segmental upright metal sections;means disengageably interconnecting said sections with their uprightedges spaced circumferentially from each otherrto form elongated slots;a lining of refractory material enclosed by the interconnected sections;and electrodes mounted to extend through the slots between such uprightedges into the furnace and supported by said lining; whereby saidsections may be disconnected and removed for access to the refractorymaterial without disturbance of the electrodes.

2. In a furnace for melting refractory material, an outer casingcomprising a plurality of separate segmental upright metal sections;means disengageably interconnecting said sections with their uprightedges spaced circumferentially from each other to form elongated slots;a flange on the inner surface of each section adjacent and above itsbottom edge; a metal floor plate removably mounted on said flanges; alining of refractory material enclosed by the interconnected sectionsand supported by said floor plate; and electrodes mounted to extendthrough the slots between such upright edges into the furnace andsupported by said lining; whereby said sections may be disconnected andremoved for access to the refractory mate rial without disturbance ofthe electrodes.

3. A furnace casing as claimed in claim 2 in which each section has anangle secured along each edge; each angle having the outer edge of oneleg secured to the section with the other leg extending inwardly fromthe edge of the section; said interconnecting means comprising strapsbolted to the outer legs of adjacent angles.

References Cited in the file of this patent UNITED STATES PATENTS1,626,000 Kay Apr. 26, 1927 1,737,566 Brown Dec. 3, 1929 2,280,101Slayter Apr. 21, 1942 2,340,601 Langford Feb. 19, 1944 2,493,939 AmesJan. 10, 1950 2,538,811 Triggs Jan. 23, 1951

